The phrase "a letter requiring" is correct and usable in written English.
You can use it when referring to a letter that demands or requests something from the recipient.
Example: "I received a letter requiring my immediate attention regarding the upcoming meeting."
Alternatives: "a letter asking for" or "a letter demanding".
In 2005, Pope John Paul II wrote a letter requiring every US bishop to designate an exorcist, Thomas tells me.
No detail was too minor to escape his attention; once, while preoccupied with an important business deal, he noticed that a publisher had sent him a cover on which a Japanese life preserver bore an English name printed in tiny type, and immediately sent off a letter requiring a correction.
Carolyn Hax and Dear Prudence keep their tips practical, unless, as occasionally happens, a letter requires them to wade in with the miraculous Thor hammer of life-changing insight.
When did we decide that even a mild activity, like mailing a letter, requires a backpack with plastic bottle of water to "stay hydrated"?
If the pastor could not be contacted by phone, they were sent a certified letter requiring a signature of receipt.
A pharmacy kept the randomisation list and sent the study tablets (either valerian or placebo) as a registered letter, requiring participants to confirm receipt by signature.
For example, it allows F.B.I. agents to issue a "national-security letter" requiring a company to turn over records listing the phone numbers someone has called, although a warrant is still required to eavesdrop on the content of calls.
For the obvious reason: creating a capital letter requires an extra step, the ultimately unhip pressing of the shift key.
A warning letter requires correction of violation and a written response within 15 days of receipt of letter; otherwise, enforcement action may ensue.
One specific cue probe trial sequence requires a target response (i.e., "A" followed by "X"; AX trial), with all other combinations of letters requiring a nontarget response.
Each of the word and pseudoword lists required an equal number of "yes" and "no" responses and the position of the probe letters requiring a "yes" response was matched across lists.
